Thrombospondin deposition in rat carotid artery injury

The balloon catheter injury model was used to determine the relative contributions of vascular smooth muscle cells (SMC) and platelets to thrombospondin (TSP) antigen deposition in the artery wall. Rat carotid arteries were denuded of endothelium, exposing the thrombogenic subendothelial extracellular matrix (ECM) to the circulation. Rats were killed after 1 hour, or 5, 10, or 20 days. Thrombospondin antigen deposition in the injured arteries was assessed using a specific polyclonal antiserum raised in rabbit against rat platelet TSP and a sensitive silver-enhanced immunogold staining method. Faint immunostaining for TSP antigen was detected, associated mostly with cells, in the media of the carotid artery of the nonoperated controls. One hour after balloon catheter injury, however, prominent cell-associated immunostaining was evident in the media; extracellular matrix staining was negligible. At this time, large foci of immunostaining were present on the lumenal surface of the vessel. Intimal proliferation was evident on most stained sections of tissue taken 5 days after balloon injury. Thrombospondin antigen immunostaining was markedly increased compared to nonoperated controls in all sections, regardless of the degree of intimal thickening. Thrombospondin immunostaining remained associated with cells in the neointima and media; extracellular matrix staining remained negligible. Ten days after endothelial injury, immunostaining for TSP antigen was detected in all layers of the artery, but was greater in the neointima and media. Reaction product was still associated only with cells. Thrombospondin antigen levels, as detected by this procedure, remained high in the injured tissue through 10 days of observation but appeared less prominent 20 days after injury. At this time extracellular matrix staining was obvious and cell-associated staining was reduced. These data support the hypotheses that thrombospondin (TSP) expression by vascular smooth muscle cells is an early response to injury and that the primary source of TSP antigen in injured artery is the vascular smooth muscle cells (SMC). These results support data derived from in vitro studies of TSP secretion.